In addition to the acceleration sensors used in a central airbag control unit, at the present time peripheral acceleration sensors or pressure sensors are primarily used for sensing side crashes. The demands on crash detection are very high in the case of a side impact. Since the distance between the outer side of the vehicle and the vehicle occupant to be protected is very small, the decision about triggering or not triggering the side airbag or head airbag, for example, must be made in a very short time (e.g., 5-10 ms), so that these restraining devices can still inflate to provide protection. To achieve great robustness of the system with respect to unwanted triggerings of restraining devices, an additional, independent plausibilization circuit is used when detecting side crashes on the basis of signals from peripheral acceleration sensors. This is usually accomplished on the basis of the acceleration signal from a second acceleration sensor (e.g., positioned on the vehicle tunnel). Because of the acquisition of vehicle-dynamics data such as lateral acceleration, yaw rate, steering angle and wheel speeds possible today in vehicles having ESP (or other systems), the float angle as well as the longitudinal velocity and lateral velocity of the vehicle can be estimated. This information is also used for triggering reversible restraining devices, as well as the window lifters, the seat adjuster and the sunroof (pre-safe). However, the vehicle-dynamics information alone is not sufficient for triggering irreversible restraining devices.
German Patent Application No. DE 199 10 596 A1 describes a method and a system for controlling the triggering of restraining devices in a motor vehicle, provision being made to acquire actual values of the vehicle movement and to apply a triggering algorithm to the acquired actual values for generating triggering signals as needed for the triggering of at least one of the restraining devices. In so doing, the following steps are to be carried out: acquiring actual values of the vehicle movement; determining the setpoint state of the vehicle movement corresponding to the desired operating behavior of the vehicle; comparing an actual state of the vehicle movement, determined from at least a portion of the acquired actual values, to the corresponding setpoint state; parameterizing a triggering algorithm used for generating triggering signals, taking into account deviations between the actual state and the setpoint state of the vehicle movement; and application of the triggering algorithm to at least a portion of the acquired actual values for generating situation-adapted triggering signals as needed for triggering at least one of the restraining devices.
International Application WO 90/09298 also describes a method for triggering restraining devices in a safety system for vehicle occupants, in which an acceleration signal is measured, this acceleration signal is converted by time integration into a velocity, and in which at least one threshold value is specifiable for the velocity for forming a triggering criterion. In this method, the threshold value used as triggering criterion is moreover alterable as a function of one or more state variables or past state variables of the vehicle.